1. Field of the Invention
The present disclosure relates to a driving assistance device that assist a vehicle in driving.
2. Description of Related Art
A driving assistance device is known as a device used to assist in keeping a safe inter-vehicle distance between a host vehicle as an assistance object and a preceding vehicle travelling in the travel direction of the host vehicle. When performing driving assistance, such a device can detect a relative position and a relative speed of an object in front of the vehicle's travel direction, thereby identifying the presence of a preceding vehicle. Moreover, the device performs an inter-vehicle control (speed control), to make the host vehicle follows the identified preceding vehicle. For example, Japanese Patent Application Publication No. 2007-176290 (JP 2007-176290 A) discloses an example relating to such a driving assistance device.
The driving assistance device disclosed in JP 2007-176290 A includes: host vehicle driving information detection means for detecting the host vehicle's travelling information; preceding vehicle information detection means for detecting the preceding vehicle information as travelling information of a preceding vehicle relative to the host vehicle. Also, the device includes steering control amount calculation means for calculating a control target value according to the positions of the preceding vehicle and the host vehicle, and calculates a steering control amount for following the preceding vehicle with a feedback control which is based on the control target value. Moreover, the driving assistance device also includes control gain setting means for temporarily decreasing the control gain of the feedback control when the preceding vehicle detection means detects that the preceding vehicle is switched. By such a configuration, an assistance to control an inter-vehicle distance between the host vehicle and the preceding vehicle is performed.
According to the driving assistance device disclosed in JP 2007-176290 A, when a vehicle enters between the host vehicle and the preceding vehicle, the control gain of the feedback control is decreased, thus, a sudden performing of a strong driving assistance caused by the entering vehicle mostly detected in a position near the host vehicle is restrained. Besides, by restraining the rapid change during the driving assistance, the uncomfortable feeling of the users brought by the assistance will be restrained.
Incidentally, the preceding vehicle switching detection of the driving assistance device etc. disclosed in JP 2007-176290 A is mostly performed by prioritizing maintaining a safe inter-vehicle distance; when the preceding vehicle is switched, sometimes, large deviation will remain between a travel trajectory of the preceding vehicle before switching and a travel trajectory of the preceding vehicle after switching in a width direction of the host vehicle. Therefore, due to the switching of the preceding vehicle, even if the control gain decreases, it is concerned that the driving position of the host vehicle greatly moves (unsteadiness) in the width direction of the host vehicle from the travel trajectory of the preceding vehicle before the detected switching to the travel trajectory of the preceding vehicle after switching.